Calculate current of any transformer in just 2 steps.

An electrical engineer should be able to calculate current of any transformer as quick as possible. And in industry it is the expected thing from an electrical engineer, so make sure you will read it carefully.

Calculating current of transformer is an important thing because it will decide the fuse rating required to protect the transformer from different faults. It is also important because the numerical relay setting also depend on the current that we are going to calculate.

So here are the simple steps to calculate the primary current of any transformer,

Step 1

Get the following data

1. Primary voltage.
2. Kva or Mva rating.

Step 2

Put the values in the following formula

For 3 phase

KVA = √3*V*I/1000

So to calculate current,

I = KVA*1000/√3*V

For 1 phase

KVA = V*I/1000

So to calculate current,

I = KVA*1000/V

That’s all; it will give you your transformers primary current.

Let’s take an example to get the things more clear.

• A 100 kva transformer with the voltage rating of 11000/440V, calculate the primary current to decide the fuse rating.

Step 1

Get the data,

KVA = 100 

Vp = primary voltage = 11000 volts

Step 2

Calculate the current using the formula.

I = KVA*1000/√3*V

I = 100*1000/√3*11000

That will give us,

I = 5.25 amps.

This is your primary current.

Now to calculate current of for example say 400 KVA transformer you can just multiply 5.25*4 that will give you current of that transformer equal to 21amps, and that's quick, isn't it?

calculate it by formula you will get the same answer.

you can also watch the video of the same, here :

https://www.youtube.com/watch?v=8_zWpl8mPkQ

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